1. Field of the Invention
The present invention relates to a gas appliance judgment apparatus and judgment method used in a gas meter or the like which is disposed in a gas supply line to a domestic dwelling and has a gas flow meter, and more particularly it relates to technology which enables the provision of higher advanced safety functions and services which are appropriate to gas appliances by identifying the type of gas appliance in use and identifying the presence or absence of a gas leak.
2. Description of the Related Art
A gas meter incorporating a gas flow meter is installed at the inlet port of the gas supply line to a domestic dwelling. The gas meter measures the gas flow volume passing through the gas supply line, and the measured gas flow volume is used to calculate a periodic gas billing amount. In addition to basic functions, such as measuring the gas flow volume, the gas meter also has a safety function for shutting off the gas supply when an abnormal state occurs. This safety function is a function which shuts off the gas by means of a shut-off valve provided in the gas flow path of the gas meter, in response to the detection of an abnormal usage state, for instance, if an earthquake is detected, if there is a gas leak or if the appliance is left without turned off, and the like.
FIG. 14 is a diagram showing the safe continuous use time settings employed in a shut-off function in the event that the safe continuous use time has been exceeded, which is one of the safety functions described above. This function is a function whereby, in cases where the occurrence of a gas flow has been detected and the gas flow is used continuously thereafter, then if the continuous use time has become excessively long, it is considered that an abnormal usage state of some kind, such as a gas leak, has occurred, and hence the gas is shut off.
As shown in FIG. 14, a large-scale water boiler which uses a large gas flow volume is only used continuously for approximately 30 minutes, whereas a stove which uses a small gas flow volume may be used continuously for a long period of time, and therefore based on this premise, the safe continuous use time is set to a short time when the gas flow volume is large and the safe continuous use time is set to a long time when the gas flow volume is small.
The gas meter judges that a gas appliance of some kind has started to be used, when a gas flow volume has occurred and or when the gas flow volume has changed into an increase, and based on this judgement, measures the time during which this flow rate continues. If this flow volume continues for a time exceeding the safe continuous use time shown in FIG. 14, then the gas meter shuts off the gas for safety reasons. Consequently, rather than identifying the gas appliance in use, a shut-off due to over-run of the safe continuous use time is implemented, on the basis of the used gas flow volume.
However, as shown in FIG. 14, in the small gas flow range, there are gas appliances of a plurality of types which have significantly different use times, such as stoves which are used for a relatively long period of time, and cooking stoves or small water boilers which are only used for a relatively short period of time, or the like. In the case of a conventional gas meter, it is not possible to identify the type of gas appliance in use, and therefore the safe continuous use time for this flow volume range is set to a relatively long time to match the stove which is used for a long period of time. The safe continuous use time which is set to a long time in this way is excessively long for a cooking stove or small water boiler which are situated in the same flow volume range, and therefore it does not necessarily represent the optimal safe continuous use time. In other words, this method does not identify the type of gas appliance in use and therefore it has difficulty in providing a safety function which is suited to the type of gas appliance.
From the viewpoint of overcoming the problems described above, proposals relating to gas appliance judgment apparatuses have been made in the prior art, as described in Japanese Patent Application Publication No. 2003-149019, Japanese Patent Application Publication No. 2003-149027 and Japanese Patent Application Publication No. 2003-149075, for example. In these prior art technologies, in order to identify the type of gas appliance in use from the change in the gas flow volume when the gas appliance is used, the type of gas appliance is identified by a method of the following kind, based on the concept of a partial flow volume pattern in which a complex sequence of changes in the gas flow volume is divided into respective combustion control steps.
In other words, firstly, partial flow volume patterns are classified according to control steps for a plurality of types of gas appliances which may be used, and these patterns are recorded in a flow volume pattern table. Furthermore, the combination of partial flow volume patterns corresponding to a plurality of different gas appliances is recorded in an appliance table. A partial flow volume pattern which matches a gas flow volume pattern determined by the gas flow meter is extracted from the flow volume pattern table, and furthermore, a gas appliance which matches the extracted combination of partial flow volume patterns is extracted from the appliance table.
In this prior art technology, the complex sequence of gas flow volume patterns which accompany the combustion control of a gas appliance are simplified into partial flow volume patterns which are split into respective control steps, and therefore matching with the determined gas flow volume pattern can be carried out readily and the type of gas appliance can be identified.
In particular, the inventions described in Japanese Patent Application Publication No. 2003-149019, Japanese Patent Application Publication No. 2003-149027 and Japanese Patent Application Publication No. 2003-149075 identify a gas appliance on the basis of at least three flow volume patterns occurring at respective combustion control steps: “ignition”, “initial transient period after ignition” and “stable period after stabilization of flow volume”. Furthermore, in addition to these flow volume patterns, the flow volume range is monitored in each control step, and the appliance is also identified by considering whether or not the flow volume of the determined gas flow volume pattern corresponds to the flow volume range recorded previously in the appliance table.
Although it is true that the prior art technology described in Japanese Patent Application Publication No. 2003-149019, Japanese Patent Application Publication No. 2003-149027 and Japanese Patent Application Publication No. 2003-149075 detailed above is suitable for identifying certain types of appliances which have flow volume patterns having clearly defined characteristics, since the gas appliance is always identified only on the basis of a partial flow volume pattern (or the partial flow volume pattern and the flow volume range), then this cannot be regarded as suitable judgment technology for circumstances where a large variety of gas appliances are used, as is current custom.
In particular, in the case of appliances which produce large variations in the flow volume, such as a cooking stove, a water boiler, or a bath heater, which have conventionally been used widely in normal homes, it has been possible to identify the appliance simply by monitoring the flow volume pattern and range, but in the case of appliances which show little variation in the flow volume over a long period of time, such as floor heaters where are used in most recent dwellings, it has been difficult to identify the appliance and to determine leaking simply by monitoring the flow volume.
Furthermore, there is a great difference in the flow volume pattern during use, between an appliance which does not have a governor (pressure regulator) for automatically regulating the flow volume and pressure and which is simply controlled by manual adjustment, such as a cooking stove, and an appliance which is fitted with a governor, such as a fan heater. Therefore, it has been difficult to identify the appliance simply by monitoring the range and variation of the flow volume. In the prior art, methods have also been proposed for identifying whether an appliance is fitted with a governor, is not fitted with a governor, or whether there is a gas leak, by comparison with flow volume change patterns in the event of a pressure drop, and flow volume values which have been measured in the past (for example, see Japanese Patent Application Publication No. 2005-331373), but when using a method of this kind, if there is a gas leak, or if a gas appliance not fitted with a governor is used continuously, the range and pattern of the flow volume will continue in an unchanging state in both cases, and therefore it is difficult to distinguish between these cases.